1. Field of the Invention
The present invention relates to a space diversity reception type automotive antenna system.
2. Description of the Prior Art
Antenna systems are essential for modern automobiles which must positively receive radio or other waves at their built-in receivers. Antenna systems also are very important for citizen band tranceivers each of which is used to effect the transmission and reception of waves between an automobile and other stationary or moving stations.
There is known a pole type antenna which projects outwardly from the vehicle body and which exhibits favorable reception performance. However, the pole type antenna tends to interfere with the aesthetic design of automobile.
Radio waves belonging to relatively high frequency bands, for example, VHF bands are higher in straight-advancing property. Direct waves tends to interfere with waves reflected by buildings and/or mountains to create a distortion in waves or multi-path noise by which voice signals are instantaneously interrupted. A single pole antenna cannot reduce the multi-path noise resulting from high frequency band reception.
Since the pole type antenna is directional, moreover, the reception of waves is varied each time that the direction of the moving automobile is changed relative to the incoming waves. It is therefore difficult to receive radio or waves steadily at the moving automobile utilizing a single pole antenna.
To overcome such a problem, there has been proposed a diversity reception type automotive antenna system comprising a pole antenna and rod-like sub-antenna which are spaced from each other. The antenna which can more efficiently receive waves at a particular time is automatically selected to improve the directional pattern of the entire antenna system.
The provision of an antenna rod other than the main pole antenna on the vehicle body is undesirable, because it complicates the installation of the automotive antenna system and also further damages the aesthetic appearance of the vehicle body.